洱海三种生活型水生植物叶片中碳、氮与总酚含量的比较研究

植物体内的C、N和总酚是影响其被牧食和凋落物降解的重要因素,从而影响C和N在食物链的传递和生物地化循环。本研究测定了云南洱海3种生活型（挺水、沉水和浮叶）26种水生植物叶片中C、N和总酚含量以及C/N比率,并分析了它们与总酚的关系。结果表明:挺水植物叶片的C、N和总酚平均含量为448.08、39.30和24.70 mg/g,浮叶植物叶片的C、N和总酚平均含量为433.32、35.16和28.05 mg/g,沉水植物叶片的C、N和总酚平均含量为378.36、27.31和10.28 mg/g;总体上看,植物叶片C和N含量:挺水植物 浮叶植物 沉水植物;挺水和浮叶植物叶片的总酚含量差异不显著,且均远高于沉水植物叶片的总酚含量;26种植物叶片中C和N与总酚含量均呈显著正相关。在富营养化条件下,3种生活型植物所处生境的光照和CO2供给均差异显著,会对这些植物叶片的C、N和总酚含量有一定影响,此外由于应对生境中的胁迫（草食性昆虫、病原体及紫外线辐射等）压力以及自身的生长策略的不同也可能导致C、N和酚在三者中形成差异;通过对13种沉水植物叶片总酚含量比较,推测光叶眼子菜和微齿眼子菜较为适合作为洱海耐牧食恢复先锋物种;N与总酚正相关的关系可能在富营养化进程中加速湖泊沼泽化。     

光氧环境对紫色硫细菌YL28去除无机三态氮的影响

【背景】光和氧是制约光合细菌生长代谢进而影响其除氮效果的重要因素。不产氧光合细菌紫色硫细菌——海洋着色菌(Marichromatium gracile) YL28能以亚硝氮为唯一氮源进行光合生长,对高浓度无机三态氮具有良好去除能力。【目的】阐明YL28菌株除氮效率与光氧环境的交互联系,获得其生物除氮的最适光氧条件。【方法】以高浓度无机三态氮共存海水水体为研究体系,在有光/无光条件下考查装样量(表征体系溶氧状态)对YL28菌株生物除氮活性的影响,并通过响应面分析法对装样量、光照强度和光周期3个主要因素进行优化。【结果】光照且氧浓度较低时(80%装样量),YL28具有最佳生长和无机三态氮去除能力;装样量在10%-100%时,菌体生物量(OD_(660))在0.938-2.719之间,当氨氮、亚硝氮和硝氮分别为7.16、5.67和4.83mmol/L时,其去除率分别在71.44%-89.09%、99.22%-99.83%和91.60%-97.33%。黑暗条件下,装样量在20%-100%时,氨氮、亚硝氮和硝氮去除率分别在48.07%-64.27%、73.51%-86.42%和42.57%-46.34%,但菌体生物量(OD_(660)为0.615-0.903)明显降低。通过响应面优化,当装样量、光照强度和光周期分别为80.0%(溶氧量约为0.32 mg/L)、2 800 lx和24L:0D时,细胞生长和氨氮去除活性达到最佳状态,分别比优化前提高了21.28%和14.11%。在实际应用中,选取72%-89%装样量(溶氧量约为0.26-0.63mg/L)、2240-3460lx光照强度和21L:3D-24L:0D光周期,细胞活性可达95%以上。【结论】80%装样量有助于促进菌体光照生长和除氮;在黑暗有氧和无氧环境下,YL28菌株也具有较好除氮活性,这为不产氧光合细菌在生物反应器中高效去除无机三态氮的应用提供了有价值的参考数据。     

Some Nutritional Factors Affecting Production of Biomass and Antifungal Metabolites of Coniothyrium minitans

The ability of the mycoparasite Coniothyrium minitans to utilize a range of C and N sources and vitamins for growth, pycnidial formation and antifungal metabolite production was examined using a defined liquid medium. Coniothyrium minitans was able to use all the C sources tested, with the exception of D -xylose, and all the N sources tested, although growth was generally better on organic N sources rather than NO 3 -N. Increasing C:N ratios from 9:1-202:1 with N constant (2.0 g L -l L -alanine) resulted in steadily increasing yields, whereas increasing C:N ratios with C constant (40.0 g L -l D -glucose) gradually decreased yield. Addition of thiamine to the glucose-alanine basal medium resulted in the greatest increase in growth but biomass was still less than that achieved using an undefined molasses-yeast medium. Pycnidial production was generally low or failed to occur in the basal medium + C + N sources in the absence of vitamins, but addition of thiamine consistently led to abundant pycnidial formation. Molasses-yeast static culture provided greater biomass and conidial yields than molasses-yeast shaken culture. Incorporation of C. minitans culture medium into potato dextrose broth (10% v/v) resulted in consistent reduction in growth of Sclerotinia sclerotiorum irrespective of C, N or vitamin content of the basal medium or whether molasses-yeast medium was used. This is the first report of consistent production of antifungal metabolites by C. minitans .     

Nutritional Requirements of the Nematophagous Fungus Hirsutella rhossiliensis

Six natural media were examined for growth and sporulation of six isolates of the nematophagous fungus Hirsutella rhossiliensis , using solid and/or liquid culture. Twenty carbohydrates, 19 nitrogen (N) compounds, and nine vitamins were also tested for their effects on growth, sporulation, and spore germination of a further three isolates (ATCC46487, OWVT-1 and JA16-1). Variations in nutritional requirements existed among the fungal isolates. In general, V-8 juice agar (VA), cornmeal agar and potato dextrose agar were good media for growth, and malt extract agar, VA and yeast dextrose agar were good for sporulation of all six isolates. Glycogen was the best and sucrose, inulin, D- ( + ) - trehalose and soluble starch were also good carbon (C) sources for growth and spore germination of the three isolates ATCC46487, OWVT-1 and JA16-1 in both liquid and solid culture. None of the isolates utilized D- ( + )xylose as a C source. L- sorbose, D- ribose, citric acid and D- fructose were poor for growth of all isolates. The best C source for sporulation was D- ( + )-trehalose for ATCC46487, D- sorbitol for OWVT-1 and D- ( + )-cellobiose for JA16-1. Casein was the best N source for growth of ATCC46487 and OWVT-1, while peptone was best for JA16-1. L- asparagine, L- proline, and peptone were also good for growth of all three isolates. L - cystine was not utilized by H. rhossiliensis and DL- methionine inhibited growth of all isolates. Spore germination of all isolates was well supported by most N compounds examined but was inhibited by L- cystine. No significant difference in sporulation of ATCC46487 was observed among the N sources. DL- threonine was the best N source for spore production by OWVT-1 and L- phenylalanine was best for JA16-1. Vitamins generally enhanced fungal growth and sporulation, with thiamine having the greatest influence. Excluding some vitamins individually from the medium containing all other test vitamins sometimes increased growth and/or sporulation of certain isolates.     

Aluminium Stress Affects Nitrogen Fixation and Assimilation in Soybean (Glycine max L.)

Nitrogen fixation and assimilation in nodules and roots were studied in soybean (Glycine max L.) exposed to different levels of aluminium (Al) stress (0, 50, 200 and 500 μM). Al at 500 μM induced oxidative stress, which became evident from an increase in lipid peroxidation accompanied by a concomitant decline in antioxidant enzyme activities and leghaemoglobin breakdown. Consequently, there was also a reduction in nitrogenase activity. However, the leghaemoglobin levels and nitrogenase activity were unexpectedly found to be higher in nodules when the plants were treated with 200 μM Al. Of the enzymes involved in nitrogen assimilation, the activity of glutamate dehydrogenase-NADH was reduced in nodules under Al stress, but it was significantly higher in roots at 500 μM Al as compared to that in the control. In nodules, the glutamine synthetase/glutamate synthase-NADH pathway, assayed in terms of activity and expression of both the enzymes, was inhibited at >50 μM Al; but in roots this inhibitory effect was apparent only at 500 μM Al. No significant changes in ammonium and protein contents were recorded in the nodules or roots when the plants were treated with 50 μM Al. However, Al at ≥200 μM significantly increased the ammonium levels and decreased the protein content in the nodules. But these contrasting effects on ammonium and protein contents due to Al stress were observed in the roots only at 500 μM Al. The results suggest that the effect of Al stress on nitrogen assimilation is more conspicuous in nodules than that in the roots of soybean plants.     

Prevalence of nitrous oxide reducing capacity in denitrifiers from a variety of habitats

Summary A total of 81 strains isolated by T. N. Gamble from soils from eight countries, fresh water lake sediments and nitrified poultry manure were examined for their ability to grow on N₂O as their electron acceptor, as well as for their tendency to produce N₂O from NO ₃ ⁻ in the absence and presence of acetylene. Seventy-seven of the 81 strains were confirmed as denitrifiers. Fifty-nine of the 77 strains grew on N₂O, while 12 strains produced N₂O but could not utilize it. Six strains reduced NO ₃ ⁻ to N₂ but could not grow on N₂O, suggesting that even if N₂O is always an intermediate product of denitrification, it is not always a freely diffusible intermediate. The organisms, however, would consume N₂O that accumulated early in growth and accumulated N₂O in the presence of acetylene. Thus the total number of N₂O users was 65 strains or 83% of the total tested. This implies that the N₂O reducing capacity of denitrifiers occur widely in nature. A high proportion ofPseudomonas fluorescens biotype II reduced N₂O. The accumulation of N₂O from NO ₃ ⁻ in the presence of acetylene provides strong evidence that N₂O is generally an intermediate in denitrification as well as provides additional support for the usefulness of this chemical as a general inhibitor of N₂O reduction.     

Tannin,nitrogen, and cell wall composition of green vs. senescent Douglas-fir foliage

Summary Tannin, cell wall, and nitrogen composition of green foliage and needle litter of similar-aged Douglas-fir (Pseudotsuga menziesii Mirb. Franco) from two stands differing in density and crown closure were compared. Trees in the closed-canopy stand had a lower basal area growth rate than those in the open-canopy stand. Stands did not differ in wood basal area/ha or forest floor C/N ratios, but the closed-canopy stand had a significantly larger accumulation of forest floor biomass and significantly higher levels of field-extractable nitrogen and nitrogen mineralization rates. Green foliage from trees in the closed-canopy stand had significantly lower nitrogen, astringency, and lignin contents, but higher cellulose concentration than trees in the open-canopy stand. These trends, inconsistent with the inverse relationship often observed between nitrogen and polyphenol contents of foliage, may result from differences in relative resource availability in the two stands. In contrast to green foliage, needle litter from the two stands had comparable contents of nitrogen, cellulose, and lignin, but astringency was significantly higher in litter from the closed-canopy stand. It is suggested that, within the constraints imposed by site conditions, evergreens may alter the tannin composition of senescing foliage, potentially affecting herbivory and decomposition differently.     

Arbuscular mycorrhizal fungi modulates dynamics tolerance expression to mitigate drought stress in Ephedra foliata Boiss

Arbuscular mycorrhizal fungi (AMF) are one of the most important drivers of soil ecosystem dynamics. AMF have the potential to improve plant growth and development by modulating key hormonal pathways, which result in decreasing the adverse impact of abiotic stress, such as drought. Pot experiments were conducted in this study to investigate the ability of AMF to ameliorate the adverse impact of drought in Ephedra foliate. Non-inoculated AMF E. foliate (Ef) plants, exhibited reduced growth in response to drought stress with a concomitant lowering of chlorophyll pigments, relative to non-stressed and AMF inoculated plant. AMF inoculated E. foliate showed improved nitrogen metabolism by positively regulating nitrate and nitrite reductase activity which results in greater ammonium availability for the synthesis of amino acids. Inoculation with AMF also increased antioxidant enzyme activity, ascorbic acid contents, and reduction in glutathione level. This resulted in significant amelioration of oxidative damage to plant membranes by restricting the excess generation of reactive oxygen species (ROS), such as hydrogen peroxide. Greater content of proline, glucose, and total soluble protein in AMF-inoculated plants provided further benefit to E. foliate plants and their ability to withstand drought stress, and also evident by a greater level of sucrose phosphate synthase activity. AMF significantly enhanced the uptake of essential nutrients like K, Mg, and Ca. Importantly, higher concentrations of plant hormones, including indole acetic acid (IAA), indole butyric acid (IBA), gibberellic acid (GA), and abscisic acid (ABA), were maintained in AMF-inoculated Ef plants. AMF inoculation also boosted phosphorous metabolism by increasing alkaline and acid phosphatase enzyme activity. In summary, AMF-inoculation of Ef plants significantly reduced the deleterious effect of drought stress by up-regulating the antioxidant defense system, synthesis of osmolytes, and maintaining phytohormone levels.     

Effects of manganese-supplemented diets on growth performance,blood biochemistry,nitrogen metabolism and skeletal development of rex rabbits

(Background) Manganese (Mn) is an essential mineral, although its effects on rabbits is not clear. (Research Purpose) This study was conducted to investigate the effects of the level of supplementation of dietary manganese on growth performance, blood biochemistry, nitrogen metabolism and skeletal development of growing Rex rabbits. (Methods) Two hundred 3-month-old healthy Rex rabbits with similar body weights were randomly divided into 5 groups (A, B, C, D, E), with 40 replicates in each group. The rabbits in the 5 groups were fed a basal diet containing 0, 5, 10, 20 and 40 mg/kg manganese (in the form of manganese sulfate), respectively. The trial included 7 days for adaptation and 29 days of testing. Seven days before the end of feeding, eight rabbits from each group were transferred into a metabolic cage for metabolic testing. (Results) The results showed that supplemental dietary manganese levels did not significantly influence final body weight (FBW) or average daily feed intake (ADFI) (P＞0.05). Average daily gains (ADG) were significantly higher in the 20 mg/kg manganese group than in the other groups, and the ratio of feed to body weight gain (F/G) was significantly affected by manganese level (P < 0.05). No significant differences were found in the digestion coefficients among the groups (P > 0.05). Regarding carcass traits, the thymus index and total fat were significantly different (P < 0.05) among the groups, but there were no other significant differences (P > 0.05). The addition of manganese had no significant effect on the intake of nitrogen (IN), fecal nitrogen (FN), digestible nitrogen (DN) or the apparent digestibility of nitrogen (NAD). Compared to the other groups, urinary nitrogen (UN) was lower in the 20 mg/kg group, although nitrogen deposition (RN), nitrogen utilization (NUR) and the biological potency of nitrogen (NBV) were higher in this group (P < 0.05). As the amount of manganese added to the diet increased, serum triglycerides decreased (P < 0.05). Serum Mn-SOD was significantly lower in the 5 mg/kg manganese group than in the other groups (P < 0.05). The results of this study demonstrate that a diet with supplemented manganese can improve Rex rabbit growth performance and increase RN, NUR and NBV. There were no significant effects of different dietary levels of Mn on the ratio of bone to meat (P > 0.05) or bone strength (P < 0.05). (Conclusion) In conclusion, we determined that the optimal level of manganese supplementation in the diet of growing Rex rabbits was 20 mg/kg, which was also found to reduce nitrogen emissions into the environment.